Expansion valves are currently commonly used in compression-type refrigeration circuits.
In particular, two-way valves are used to control the flow of refrigerant by means of an orifice and a flow control element, which is preferably actuated by means of an electric motor drive.
These thermostatic expansion valves are designed to control the flow of refrigerant that circulates.
A flow-rate adjustment valve for fluids, particularly refrigeration fluids, servo-controlled with an electric motor has been devised and is disclosed in EPA-99101786.4 of 15 Feb. 1999 and in U.S. Ser. No. 09/250,251 of 16 Feb. 1999.
Said valve comprises a valve body provided with intake and discharge ports, which is closed reversibly by a flow control element; the valve has a driver section for actuating and adjusting the flow control element, in which the rotor component of the motor is supported rotatably within a hermetic capsule which is fixed to the valve body.
The rotor component, which is fixed axially, has a screw-and-nut coupling to a part of the flow control element, which is rigidly coupled to the valve body so as to perform only axial translational motions.
Said valve is capable of providing a fine adjustment of the degree of closure without triggering dangers of damage or wear of the edges related to the orifice to be closed.
Another particularity of said valve is that it can be adapted also to refrigeration systems that have already been installed and ensures in the most absolute way an outward hermetic seal for the refrigeration fluids that flow therein.
Although this valve is appreciated and widespread, it has aspects that can be improved.
A first important drawback is the mismatch of the position of the means for reducing rotary friction, generally a ball bearing, that support the rotor component, with respect to the coupling between the threaded portion of the stem of the flow control element and the corresponding female thread formed inside the rotor component.
This mismatch in an axial direction of the screw-and-nut coupling with the position of the ball bearing causes the radial components of the pressure applied by the fluid to the tip of the open flow control element to be imperfectly balanced by the contrasting axial thrust of the bearing, consequently generating a torque which misaligns the axis of the flow control element with respect to the correct direction of advancement and with respect to the correct axis of rotation.
This misalignment can compromise the correct and efficient operation of the valve, because it leads to friction of the magnetic cylindrical element of the rotor component against the internal surface of the capsule and simultaneously, by offsetting axially the rotor component with respect to the stator component of the electric motor, it prevents the optimum closure of the magnetic circuit on these components, with consequent irregularities for the opening-closing movement of the flow control element.
Further, said known valves have different dimensions depending on the uses for which they are intended, with consequent differentiation in the shape and dimensions of the flow control elements provided therein.
This differentiation among flow control elements of valves, which are equivalent in terms of functionality but are dimensionally different, entails as many different operating sequences as there are flow control element models, with consequent management costs for both storage and assembly.